Closed hemapheresis system and method

ABSTRACT

A centrifugal separator system is provided for extracting lighter matter from a liquid suspension. The separator includes a housing having an axis, an inlet port, a lighter matter outlet port and a heavier matter outlet port spaced from the inlet port. A rotatable interior double shell rotor is disposed within the housing. The rotor includes outer and inner shells and defines a centrifugation gap therebetween. The rotor is spaced from the housing by a flow gap. The outer shell includes means providing communication between the centrifugation gap, the inlet port and the heavier outlet port. Means are provided in the double shell rotor for conducting lighter matter from the centrifugation gap to the lighter matter outlet port.

This is a continuation of U.S. patent application Ser. No. 06/644,032,filed on Aug. 24, 1984, now U.S. Pat. No. 4,776,964.

BACKGROUND OF THE INVENTION

This invention relates to the separation of one or more constituents ofblood, and is more particularly directed to a closed system employingcentrifugal force for separating different constituents from whole bloodbased on density or size, such as the separation of platelets and plasmafrom whole blood, ad to the method for carrying out such separation.

Whole blood consists broadly speaking of red blood cells, white bloodcells, platelets and plasma. Hemapheresis, which is directed to theseparation of one or more constituents of blood, encompasses theextraction of many different constituents in the present state of theart. Plasma, for example, is separated from whole blood taken fromdonors and stored, with the packed cell remainders from the blood beingreturned to the donors. Red blood cells are concentrated and stored orreused, sometimes being held in frozen state before reuse.

There are numerous therapeutic apheresis applications under study inwhich, using temporary or permanent separation of blood constituents,treatments or procedures are applied with sometimes dramatic benefit inamelioration of specific diseases or afflictions. It is sometimesdesirable to separate leukocytes (white cells) from the red blood cells.In other instances it is sought to extract platelets, which have aprincipal role in the clotting function, from red blood cells, with orwithout plasma. In all of these applications, the fragile blood tissuemust be handled in a non-traumatic manner to avoid the introduction ofhemolysis or the initiation of the clotting action.

Hemapheresis has heretofore principally been carried out usingcentrifugation techniques, or membrane filtration systems. Spinningwhole blood in a centrifuge at an appropriately high rate separatesconstituents in accordance with their density, and by using asufficiently high rate and an adequately long period of time a finediscrimination in constituents, in accordance with density, can beachieved. Batch centrifugation, however, is cumbersome and lengthy andnot suitable for many applications in which it is desired to extractmore than one constituent or return packed cells or other constituentsto a donor.

Accordingly, cell separators have been developed and are in use, such asthe Model 30 offered by Haemonetics Corp. for cell extraction. Thisincludes a disposable unit comprising a rotatable rotor with an interiorcore so configured that heavier matter moves to the outside diameter ofthe rotor/core combination, causing lighter matter to pass throughinterior ports to an outlet. To achieve appropriate centrifugationforces so as to separate materials that are quite close in densityrequires high speed operation, and this device must be run for asubstantial period of time before separation occurs. The Haemoneticsunit accordingly is driven at approximately 4800 rpm and is quiteexpensive (in the range of $45.00 per unit) for a disposable device. Thegreat majority of such hemapheresis units are disposables that are usedonly once, because of the likelihood of transmission of infectiousagents from one donor to another.

Furthermore the Haemonetics device is regarded as an open pathconfiguration, in that the inlet and outlet paths for the constituentscan communicate with the exterior environment through rotary seals.Microbe infiltration is a danger with such open systems, in consequenceof which the FDA requires that the extracted matter be used within 24hours to avoid the possibility of contamination.

Membrane filtration using a spinning rotor within a concentric shell hasnow been shown to be extremely effective for separating someconstituents of blood from others, as for example separation of plasmafrom leukocytes, platelets and red blood cells. There is a substantialdifference in density and in tee size of the elemental plasma whichpasses through the membrane relative to the cellular matter which is notfiltered. However, when it is desired to separate certain cellularmatter from other cellular matter, sizes may vary but little, as in thecase with platelets which are of only slightly lower density incomparison to red blood cells. Membrane filtration does not appear to beappropriate for performing this function. Yet for certain applicationsit is of importance to extract platelets separately, and for others toprovide a platelet rich plasma.

There is therefore a widespread need for a closed system and method thatwill separate different constituents of whole blood that aredifferentiable in density and size, but only in a minor degree, and tobe able to do so with a relatively low cost disposable unit that isclosed to the exterior environment. A further aim is to provide a closedsystem and method for the separation of platelet rich plasma from wholeblood.

SUMMARY OF THE INVENTION

A hemapheresis system and method in accordance with the inventioncomprises a stationary housing that has an inner wall concentric about acentral axis, and upper and lower ports communicating with the interiorof the housing. Within the stationary housing is a double shell rotorconcentrically mounted and rotatable about the central axis within thehousing. The outer rotor wall has a predetermined close relationship tothe stationary inner housing wall, permitting blood entering the housingcavity at its lower end to rise. However, blood also moves through thelower part of the rotor wall into a centrifugation gap defined by asubstantially concentric inner wall or core, and advances upwardly whilebeing subject to centrifugation action. The residence time androtational rate are selected such that near the top of the rotor heaviercellular mater is concentrated at the outer radial region. From thisupper region the heavier matter is withdrawn through orifices in thewall that communicate with the upper outlet port in the housing. Lightermatter moves upwardly over the top of he core to a central orifice whichpasses downwardly along the central axis to a conical outlet orifice.Means associated with the gap between the rotor and housing limit upwardblood flow in this gap by creating a differential flow impedance, makingthe centrifugation gap the preferred passageway. The system thuscontinuously separates the majority of the input whole blood into thedesired fractions.

This system is biologically closed inasmuch as flows into and out of thestructure are made only through fixed ports and all rotary seals areinternal to housing and completely isolated from the outsideenvironment. Using a rotor of approximately 4" in diameter, sufficientcentrifugal force is generated for separation of matter such asplatelets and plasma with a relatively low rotation rate of 2000 rpm orless. In addition the structure provides continuous centrifugalseparation in a low cost, disposable unit.

Structures in accordance with the invention advantageously drive therotor on sealed internal end bearings, at least a lower one of which hasa central axial orifice to conduct plasma rich in a specificsubpopulation of blood such as platelets from the center passageway inthe rotor core to an outlet. A magnetic drive external to the housingcouples to an internal magnetic element mounted on the upper part of therotor so as to achieve the needed rotational velocity.

In one specific example of a system a differential flow impedancebetween the centrifugation gap and the rotor-housing gap is establishedby employing a bowl-shaped configuration in which blood follows acompound curvature path that expands radially outwardly in the midregion of the housing. In addition the rotor-housing gap leads to aclosed upper end. Thus, whole blood fed into the bottom of the spacebetween the rotor and housing moves through lower apertures in the rotorinto the centrifugation gap and begins rotation with and upward movementwithin the rotor. Whole blood in the outer gap rises upwardly but beingessentially stationary and acting against an enclosed volume reachesonly a predetermined level determined by the pressure needed to advanceblood to the top of the centrifugation gap. In the upper portion of therotor, the heavier cellular matter separated by centrifugationencounters apertures in the outer perimeter of a top deflector plate,allowing packed cells to pass into an upper passage and out through anupper outlet port in the housing. Lighter matter, such as platelets andplasma, migrates inwardly next to the deflector plate until it reachesthe central passageway in the rotor core and can move downwardly to thecoaxial outlet orifice.

In a second example of a system in accordance with the invention, theinner wall of the housing and the rotor are substantially right circularcylinders. The differential flow impedance is provided by a mid regionreduction in the gap between the rotor and inner housing wall, which maybe augmented by injecting a compatible fluid such as plasma or salinesolution into the narrow gap region. Here the heavier cellular mattermay continuously egress the centrifugation gap at the top end of therotor via holes in the circumference of the rotor wall to be mixed withthe small amount of whole blood passing along the rotor-housing gap.

Another aspect of the invention is that a separator as described can beutilized in conjunction with membrane filtration in a closed system, toprovide continuous extraction of packed cells and plasma for return to adonor, while separately dividing out platelets. In such a system, thecentrifugal device of the invention feeds a platelet rich plasma to amembrane filtration unit, such as a device of the type having aninterior sinner within a stationary housing. The outer wall of thespinner or the inner wall of the housing has a membrane covered surfaceand a conduit system for collecting plasma passing through the membrane.Consequently, by initial serial extraction of the platelet rich plasmafrom the whole blood and then removal of the plasma from the plateletrich mixture, one obtains the platelet concentration. As a variant onthis system, a minor proportion of plasma is returned to the donor withpacked cells by feeding a bypass plasma flow into the mid region of thecylindrical configuration of separator.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention may be had by reference to thefollowing description, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view, partially broken away, of a closed systemfor centrifugal separation of the constituents of blood;

FIG. 2 is a cross-sectional view of the arrangement of FIG. 1;

FIG. 3 is a fragmentary view of a portion of the separator of FIGS. 1and 2;

FIG. 4 is a block diagram representation of a disposable system forextraction of platelets from whole blood;

FIG. 5 is a side sectional view of a different system for centrifugalseparation of blood constituents;

FIG. 6 is a perspective view, partially broken away, of the system ofFIG. 5;

FIG. 7 is an enlarged fragmentary sectional view of a portion of thesystem of FIGS. 5 and 6, showing the manner in which separation occurs;and

FIG. 8 is a block diagram representation of a system using thearrangement of FIGS. 5-7 for taking whole blood from a donor, returningcertain fractions and collecting other certain fractions.

DETAILED DESCRIPTION OF THE INVENTION

A hemapheresis system in accordance with the invention, referring toFIGS. 1 and 2 of the drawings, comprises a biologically closed cellseparator 10 including a stationary outer housing 12, a rotor outer wall14, and a rotor core or inner wall 16 positioned within the rotor anddefining with the rotor a double shell system. These elements aremounted concentric with a central vertical axis, the verticaldisposition being referred to for convenience and ease of description inthe specification and claims. It will be appreciated from the followingdescription, however, that these systems do not require a particularorientation or gravitational effect and can be used in differentjuxtaposition than the true vertical. The space between the rotor wall14 and core 16 defines a shaped centrifuging chamber that presents alower impedance to flow than does the space between the rotor wall 14and the housing 12. The housing 12 has a relatively narrow base portion18 and an upwardly and outwardly diverging portion or bowl 20 whichextends from the base to a final, substantially vertical section. Thebase portion 18 of the housing has an inlet port 21 and a lower centraloutlet port 24 positioned adjacent to each other along the central axisof the housing. The upper end of the housing is closed by an upperhousing cap 26 connected across the end of the upwardly divergent bowl20 of the housing. The housing cap 26 includes an upwardly extendingboss at its mid region to form an upper central housing portion 28 whichterminates in an upper outlet port 30 which also extends along and iscoaxial with the central axis of the housing 12.

The rotor wall 14 has an exterior shape generally conforming to theperiphery of the outer housing 12, and includes a lower, necked down,base portion 32 and an outwardly and upwardly curved portion 34 ofdouble curvature forming a rotor bowl, the upper end of the rotor beingclosed on the outside by a horizontal rotor cap 36. The rotor wall 14 isspaced apart from the inner wall of the housing 12 to form an adequateclearance gap to receive a predetermined inlet volume of blood that isconfined principally to the lower part of the space between the housing23 and the rotor 14. Blood flowing upwardly in this space issubstantially non-rotating because of the stationary housing 12 wall andin addition acts against gas trapped in the closed upper end of therotor-housing gap, which gas acts as a compliance opposing increasedupward advance of the inlet whole blood in this space. Thus in therotor-housing gap the blood rises only to a certain level below theupper portion of the housing. The rotor cap 36 is formed with anupwardly extending central conduit 40 positioned along the central axisof the housing and the rotor, and communicating between the interior ofthe hollow rotor from the outer periphery of greatest diameter, and theupper outlet port 30 of the housing.

The rotor wall 14 is coupled to and is rotatable on upper and lower endbearings 42 and 44, respectively, that are coaxial with the centralaxis. The upper bearing 42 comprises a stationary stainless steel pivotpin having a central orifice and mounted as by a press fit in the upperoutlet port 30 on the central housing portion 28. A compliant 0-ring 48is captured between the rotatable central conduit 40 at the upper end ofthe rotor and the lower end of the pivot pin, to form an upper fluid andpressure seal between the rotor and the stationary housing. The lowerbearing 44 comprises a stationary stainless steel pivot pin having acentral orifice, fixed as by a press fit to the inner wall of the lowercentral outlet port 24. An 0-ring 52 is retained in a groove 53 formedon an upstanding central tubular portion 54 mounted on the base portion32 of the rotor. The O-ring 52 makes slidable contact with the outersurface of the pivot in the orifice of the pin 44 and can shift slightlyup and down the pivot pin in response to any limited axial motion of therotor, and maintain a fluid and pressure seal between the rotor and theouter housing wall. Leakage across the seal can only take place withinthe interior of the housing so that the flow paths are isolated fromexterior contamination. The lower end of the central tubular portion 54has a shoulder 55 which contacts the upper end of pivot pin 44 tosupport the rotor wall 14.

The base of the central tubular member 54 on the rotor includes aplurality of apertures 56 spaced circumferentially around the member 54about the pivot pin 44. The rotor 14 also includes an upper deflectorplate 58 positioned just below the rotor cap 36, and connected acrossthe upper end of the rotor in the region of greatest diameter thereof.The deflector plate 58 has a plurality of apertures 60 spacedcircumferentially around the outer diameter of the plate near the outerperiphery, and permitting flow into an upper chamber between the cap 36and the deflector plate 58.

The rotor core 16 is mounted concentrically within the interior of thehollow rotor wall 14 to rotate as part of the rotor structure. Theexterior configuration of the core 16 conforms to but is spaced apartfrom the rotor wall 14 so that the centrifugation volume has anincreasing radii of curvature as one proceeds in the upward direction.The rate of change of the radius of curvature, however, is not constant.The core 16 comprises a base portion 62 and an upwardly and outwardlydivergent portion 64 of bowl shape, a top portion 66 and a reentrantcentral conduit or passageway 68 connected to the base 62 and providinga flow path down from the top of the rotor. The central conduit 68 ofthe core includes a bottom portion 69 which is fitted around the centraltubular portion 54 of the rotor 14 structure. The space between theouter wall of the core 16 and the rotor wall 14 therefore defines asecond or centrifugation gap 70 through which the substantial majorityof the volume of liquid to be processed is conducted.

A cylindrical magnet 72 is mounted within the upper central housing 28concentrically about the central vertical axis, and is fixed as by pressfitting around the central conduit 40 at the upper end of the rotor 14.The magnet 72 when driven thus turns the rotor and the interior corewithin the upper and lower end bearings 42 and 44. An externalmagnetic-type rotary drive, indicated only generally at 74, is disposedabout the housing 28 to couple magnetically to the inner magnet 72 andprovide synchronous rotation of the entire internal structure comprisingthe rotor wall 14 and core 16, without the requirement for any directmechanical coupling.

The operation of the device of FIGS. 1 and 2 will be described hereafterin an application for the separation of whole blood into packed cellsand platelet rich plasma. By packed cells is meant the combination ofred blood cells and white blood cells, in the absence of platelets andplasma. It will be understood, however, that this is only one example ofthe application of the closed cell separator and method of the presentinvention, and other specific separation applications can be carried oututilizing the invention system.

Referring to FIGS. 1 and 2, the rotor 14 and core 16 are rotated by theexternal magnetic rotary drive 74, as whole blood enters within thestationary housing 12 through the whole blood inlet port 21. As theblood travels vertically upward into the housing interior it meets thebottom interior portion of the spinning rotor 14 and fills the gap 38between the rotor and housing, rising to a predetermined height. Thisheight is determined principally by the input pressure of the wholeblood, the rotational velocity of the rotor, the relationship betweenthe centrifugation gap and the relatively static rotor-housing gap, andthe maximum radius of the centrifugation gap, and the level of backpressure presented by the gas entrapped above the blood, in the closedend of the rotor-housing space. The whole blood also enters and fills agap 76 between the lower stainless steel pivot pin 44 and the baseportion 32 at the interior of the tubular portion 54 of the rotor. Theblood then passes through the ring of blood inlet apertures 56 into thelower end o the centrifugation gap 70 between the core 16 and the rotorwall 14. Blood in the gap 38 between the housing 12 and rotor wall 14rotates only at the rotor surface through viscous drag and thereforeestablishes a hydraulic pressure source when the operation stabilizes.

The blood is forced upwardly within the centrifugation gap 70 via theapertures 56 by the initial centrifugal forces imparted by viscous dragfrom the spinning rotor, the input pressure, and also by thecompensating hydraulic head generated by the blood level in the outergap 38. As the system continuously feeds blood into the housing at theinlet port 22, the upward flow in the gap 70 between the core 16 androtor wall 14 is continuous. As blood is impelled by centrifugal forceand feed pressure, rotational velocity increases in the mid region wherethe radius arm of the centrifugation gap 70 increases. The outward surgeof blood begins where the gap 70 turns outwardly, converting rotationalenergy of the rotor into upward movement which continues until the topportion of the rotor is reached. As previously noted, the rotor core 16is designed to provide a low volume centrifugation gap 70 in the rotor,such as a volume of the order of about 50 ml.

As the whole blood moves upwardly from the inlet apertures 56 along thecentrifugation gap 70 within the rotor, the less dense plasma portioncontaining platelets concurrently migrates toward the wall of the core16 as the denser packed cells consisting of red and white blood cellsare urged under the centrifugal forces to the outside of the gap 70. Therotor is relatively large in diameter, e.g. 4 to 5 inches, so thatadequate centrifugal force can be generated at low rpm for thisseparation to occur by the time the deflector plate 58 is reached. Witha rotor radius of 2.5 inch, at 2000 rpm there is a maximum ofapproximately 300 g for cell separation. The residence time in thecentrifugation gap is adequate for centrifugal separation of the desiredconstituents.

As shown more clearly in FIG. 3, when the whole blood being separated inthe centrifugation gap 70 reaches the upper and outermost portion orcorner of the separator volume, at 78, extraction of packed cells takesplace. At this region the more dense packed cells are quite preciselyseparated from the less dense plasma and platelets which are adjacentthe inner wall of the centrifugation gap 70. Thus the packed cells passthrough the circumferential ring of apertures 60 in the deflector plate58 into the passage 81 between the deflector plate 58 and the rotor cap36. The inlet flow pressure is adequate to urge the packed cells towardthe center of the separator until they reach and pass through the uppercentral conduit 40, pivot pin 42 and the upper outlet port 30. From theoutlet port 30 the packed cells are pumped out of the separator bysuitable pump means (not shown) or collected in a drainage bag bygravity feed.

The platelet rich plasma (plasma and platelets) at the core 16 wallpasses inwardly through the passage 83 between the top 66 of the coreand the deflector plate 58 of the rotor into the central reentrantconduit 68 within the rotor core under the feed pressure. Again, theinlet flow pressure is used to overcome centrifugal force in thisregion, although an outlet pump (not shown) can be used to assist. Thecontinuous flow, here aided by gravity, moves the plasma and plateletsdownwardly through the interior of the central tubular portion 54, pivotpin 44, and the lower outlet port 24. The platelet rich plasma is thencollected in an attached receptacle or pumped out of the separator bysuitable means (not shown).

The diameter of the ring of blood inlet apertures 56 on the rotor iskept small to enable a greater differential between the minimum andmaximum centrifuging radii. The ratio of platelet rich plasma (PRP) topacked cells removed can be controlled somewhat by using pumps toextract one or the other outlet flows at specific rates.

An important feature of the cell separator of the invention is that thewhole blood moved upwardly in the centrifugation gap 70 in the rotorwith dynamic force and for a sufficient time to achieve separationbefore it reaches the top of the gap 70. At the upper and outer region78 there is adequate gradation between the less dense platelet richplasma portion and the denser packed cell portion, to effect the neededseparation. The construction of the cell separator permits separation ofthe light density material from the heavy density material by a gentlespinning of the rotor at relatively low speeds, egg. 2000 rpm, ascompared to the speed of rotation between 4000 and 5000 rpm ofconventional cell separators.

The rotor, core and outer housing or shell of the cell separator all canbe formed of plastic and the whole device is disposable after a singleuse. Hence, the centrifugal separator device of the invention is ofsimple and economic construction.

The device of the present invention is particularly applicable to theseparation of the components of blood. The chief advantage in thisrespect is that an effective separation of blood components can beobtained using a biologically closed system, as contrasted to currentlyemployed open seal systems which are expensive. By "biologically closed"is generally meant, as with the FDA requirements, that leakage through agap between relatively moving parts is always internal to the system.Such leakage can therefore only result in mixture of differentconstituents (such as plasma and packed cells) of the whole blooditself. Exterior access is only possible at fixed ports providing inletand outlet flows and these are much more assuredly sealed. While thedevice of the invention is of particular applicability for theseparation of the packed cell portion from the platelet rich plasmaportion of whole blood, it can also be employed for extracting otherconcentrates having medical interest, including granulocytes,lymphocytes and neocytes, and can likewise have application for cellwashing and autotransfusion.

FIG. 4 illustrates another feature of the invention showing a disposablesystem which can harvest platelet concentrate, pure plasma and packedcells. In this aspect of the invention a separator 10 as illustrated inFIGS. 1 to 3 and described above is employed in conjunction with amembrane filtration unit 85 to provide continuous extraction of packedcells and plasma for return to a donor, while platelet concentrate aloneis separately collected.

In this system while blood at 86 is fed to the cell separator 10, thepacked cell output from the cell separator 10 is returned to the donorby a conduit 88 and the platelet rich plasma concentrate output from thecell separator is fed via tubing 90 to the membrane filtration device85.

The membrane filtration device has an interior spinner 92 within astationary housing 91 and the outer wall of the spinner or the innerwall of the housing has a membrane 93 covering a surface thereof and aninternal conduit system (not shown in detail) for collecting plasmapassing through the membrane. In operation, the rotating action of thespinner keep the input fluid sweeping the surface of the membrane,causing plasma to be transported through the membrane and into an outletorifice 90. The plasma output at 90 can be harvested in a separatecontainer at 95 and the platelet concentrate at 94 exiting the membranefiltration device can be collected in a container at 96.

If desired, the plasma at 90 can be returned at line 98 and through thepacked cell return line at 88, to the donor. Optionally, also, afraction of the plasma can be introduced via line 100 with the wholeblood feed at 86 to the cell separator 10, to help elutriate theplatelets from the blood in the cell separator.

The membrane filtration unit at 85 in FIG. 4 is described and claimed inthe application entitled "Method and Apparatus For Separation Of MatterFrom Suspension," Ser. No. 591,925, filed Mar. 21, 1984, by the presentinventor, which is now abandoned and suspended by file wrappercontinuation application Ser. No. 073,378 filed July 13, 1987, and isincorporated herein by reference.

FIGS. 5, 6 and 7 depict various aspects of a different biologicallyclosed system for separating lighter and heavier constituents from aninput blood flow, this configuration being of even lower cost and morecompact form. Referring now to FIGS. 5-7, the housing 110 for the systemis configured generally as a right circular cylinder having asubstantially right circular inner wall 112, a fixed inlet port 114 forblood input, e.g. whole blood, and a fixed outlet port 116 for outlet ofheavier fractions, adjacent the upper end thereof. At the bottom of hehousing 110 a fixed outlet port 118 for lighter blood fractions isdisposed concentric with the central axis of the system. In the midregion along the vertical length of the housing 110, one or more fixedinlet ports 120 for a biologically compatible fluid, such as plasma orsaline solution, is disposed at one or more points about the periphery.

Within the housing 110 a double walled rotor 126 is concentricallydisposed about the central axis, and rotatably mounted in fixed upperand lower bearings 128, 130 respectively. The lower bearing 130 has acentral orifice 132 in communication with the central outlet port 118 atthe lower end of the housing, an internal rotary seal being provided byan 0-ring 144 about the bearing 130. At the upper end of the rotor 126,a magnetic element 136 is mounted so as to be externally driven bymagnetic coupling from an external magnetic drive (not shown in detailinasmuch as it may be the same as shown in the example of FIGS. 1-3).Other types of remote drives that do not require mechanical connectionthrough the housing may also be used, although it is preferred to employthe magnetic drive inasmuch as the intention is to provide a low costdisposable. However, where other considerations prevail, a completelydifferent configuration could be used while still providing abiologically closed system, as for example a completely self-containedbattery driven motor or a motor with a power source that can beexternally energized. In other instances, where continuous separation isdesired but the system need not be biologically closed, an externaldrive directly coupled to the rotor can be used.

The outer wall 140 of the double wall rotor 126 comprises a modifiedright circular cylinder, having a gap of approximately 0.035" from theupper and lower portions of the inner wall 112 of the housing 110.However the outer wall includes an outwardly extending band 141 in itsmid region that is spaced only about 0.010" from the inner housing wall112. The rotor inner wall 142 is concentric with the opposed base of theouter wall 140 and provides a centrifugation gap 144 of approximately0.010" to 0.075", here about 0.050". Inlet apertures 146 about the lowerregion of the outer rotor wall provide an inlet path for input bloodinto the centrifugation gap region, while in the upper end of the outerwall 140 outlet apertures 148 about the periphery are in communicationwith the outlet port 116 for the heavier fraction of the fractionatedblood. At the upper end of the rotor 126 a horizontal space defines aradially inward passageway 150 between the upper end 152 of the innerwall, which merges into a central passageway 154 extending along thecentral axis downwardly into communication with the central orifice 132in the lower bearing 130, thus to define the internal core within therotor 126. The horizontal upper end wall 156 of the outer wall 140 inthis example merely serves as a closure for the internal passageways,and as a mechanical support for the magnetic element 136 and upperbearing 128.

In the system of FIGS. 5-7, the rotor is driven at a suitable rotationalvelocity, e.g. 2000 rpm, and has a length, such as 4", adequate toprovide a residence time within the centrifugation gap sufficient toprovide an adequate degree of continuous separation. To this end, wholeblood or blood constituents containing both the heavier and lighterfraction passes through the inlet port to within the housing 110. Theinput blood flow attempts to move continuously upwardly toward theoutwardly projecting band 141 on the outer wall 140 of the rotor 126,and through the inlet apertures 146 into the centrifugation gap 144. Therestricted gap between the stationary housing inner wall 112 and theband 141 on the rotor 126 and the additional infusion of a compatiblefluid introduce a substantial back pressure in this region. Thus thepreferential path for the inlet blood is within the centrifugation gap144. As is evident to those skilled in the art, plasma derived in aprocess such as that depicted and described in conjunction with FIG. 4may be used continuously as the compatible fluid input to the mid-regionports 120. Plasma input in the mid region need not be high and the onlyeffect is a slight reduction in the hematocrit of the packed cellsprovided from the outlet port 116.

Within the centrifugation gap 144, the upwardly ascending blood flow,under centrifugal force, becomes increasingly radially separated intodifferent fractions. The heaver fraction concentrates at the outer wall140, and at the uppermost region of the length of centrifugation gap144, heavier matter only is present at the outlet apertures 148. Thelighter fraction, specifically platelet rich plasma in the whole bloodexample, continuously moves inwardly along the radial passageway 150toward the central axis. Selection of the total aperture area for theoutlet apertures 148 relative to the input flow rate enables acontinuous balancing of the flows, and therefore continuous separation.The heavier fraction, such as cellular matter, combined with a smallamount of bypass whole blood and plasma traverses the outer passagewayacross the outwardly projecting surface 141. This flow is available forreturn to the donor, while the platelet rich plasma moves through thecentral passageway downwardly through the central orifice 132 and thelower bearing 130 and out the central outlet port 118 at the bottom ofthe housing 110.

The arrangement shown in FIGS. 5-7 is particularly suitable for lowcost, high volume applications. Unlike the usual centrifugationtechnique, it achieves high centrifugation efficiency by establishing arelatively thin flow path in which the radial mass that must beseparated is small, so that cells can quickly migrate to the outsideunder relatively low radial velocities. The upwardly ascending flow isat a sufficiently slow rate for the flow to be essentially laminar, sothat the centrifugation effects are not counteracted by turbulence, anda uniform outer layer of heavy matter is made available at the outletapertures in the rotor wall while the lighter fraction moves inwardly.Consequently, radial ejection of the heavier fraction is automatic andsmooth and the various geometries used in the prior centrifuge art, suchas probes or separator edges, need not be employed to divide thefractions.

The system of FIG. 8 comprises an implementation of the device of FIGS.5-7, in which plasma and platelets are separated from whole blood takenfrom a donor (not shown) with the remaining fraction being returned tothe donor. A two needle system is used, a collection needle 160 and aninput blood pump 162 feeding the blood input port 164 of a separatordevice 166 as described in conjunction with FIGS. 5-7. Anticoagulantfrom a source 170 is also added to the input blood at a controlled rateby an anticoagulant pump 172 (which along with the other pumps isdepicted schematically as a conventional peristaltic device). The outletport 174 for platelet rich plasma from the separator 166 feeds an input176 of a platelet separator 178 of the rotating spinner type, aspreviously described, via a pump 180, with the plasma filtrate beingcollected in a bag or reservoir 182 and also a portion being shunted toan input port 183 in the mid region of the separator 166. The branchedflow may be controlled by a valve or adjustable restrictor (not shown)if desired, but positive pressure is maintained by a plasma return pump184. Platelet concentrate from the platelet separator 178 is fed fromthe outlet port 186 for non-filtered remainder, as by gravity feed or apump (not shown) to a second collection bag 188.

As the separator 166 for platelet rich plasma functions, the packed celloutput from the remaining outlet port 190 is fed by a return pump 192 toa return needle 194 at the donor, or, alternatively, to a thirdcollection bag 196. Continuous operation in this manner assuresmaintenance of the desired back pressure in the mid region of theseparator 166, but it will also be understood that plasma 182 can bepumped from the plasma reservoir 182 itself if intermittent operation(e.g. a single needle system) is used.

The system of FIG. 8 is again a biologically closed, low cost,disposable system. The two separators 166, 178, three collection bags182, 188, and 196, together with interconnecting flexible conduit, areall coupled together at static joinders only. Flow rates can be matched,as shown, for continuous operation but buffer reservoirs could be usedas well.

From the foregoing, it is apparent that the present invention provides amethod and system which is effective for the separation of bloodcomponents employing a closed completely disposable system, ascontrasted to currently employed open seal systems which are expensive.

Since various changes and modifications of the invention will occur toand can be made readily by those skilled in the art without departingfrom the invention concept, the invention is not to be taken as limitedexcept by the scope of the appended claims.

What is claimed is:
 1. A centrifugal separator system for extractinglighter matter from a liquid suspension comprising:a housing having andincluding an inlet port to receive the liquid suspension, a heaviermatter outlet port axially spaced from the inlet port and a lighteroutlet port; a rotatable interior double shell rotor disposed withinsaid housing for rotation about the axis, said rotor including an outershell and an inner shell and a centrifugation gap between said inner andouter shells, said rotor being spaced from said housing by a flow gapand including means in said outer shell for providing communicationbetween the centrifugation gap and said inlet port and said heaviermatter outlet port; means within said double shell rotor communicatingwith said centrifugation gap and said lighter matter outlet port forconducting the lighter matter from the centrifugation gap to saidlighter matter outlet port; means within said housing, coupled to saidrotor, for rotating said rotor within said housing; and wherein the flowof liquid suspension is relatively unrestricted in the centrifugationgap in comparison to the flow gap.
 2. A system in accordance with claim1, wherein said rotating means coupled to said rotor means is adaptedfor rotating said rotor without mechanical connection thereto, fromoutside said housing.
 3. A system in accordance with claim 1, whereinsaid housing is a biologically closed cell.
 4. A system in accordancewith claim 1, wherein the lighter matter can be expressed out of saidlighter matter outlet port and the remainder of the liquid suspensioncan be expressed out of said heavier matter outlet port during rotationof said rotor means.
 5. A system in accordance with claim 1, whereinsaid centrifugal separator is a continuous flow separator in whichliquid suspension can be introduced into said housing through said inletport, in which the lighter matter can be expressed out of said housingthrough said lighter matter outlet port, and in which the remainder ofthe liquid suspension can be expressed out of said housing through saidheavier matter outlet port, all during rotation of said rotor means. 6.A system in accordance with claim 5, wherein said housing is abiologically closed cell.
 7. A system according to claim 1wherein saidhousing axis is a central axis, and wherein said double shell rotor isrotatable concentrically about said central axis.
 8. A continuous flowcentrifugal separator comprising:a fixed housing disposed about an axisand having an inlet port, an outlet port for heavier matter that isaxially spaced from the inlet port and an outlet port for lightermatter; and a rotor disposed within the housing for rotation about theaxis, the rotor having an outer shell and an inner wall spaced radiallyinward from the outer shell to define therebetween a gap which extendsaxially between the housing inlet port and the housing heavier matteroutlet port, the outer shall having at least one shell inlet porttherein to provide communication of fluid from the housing inlet portinto the gap, at least one shell heavier material outlet axially spacedfrom the shell inlet port in a direction toward the housing heaviermaterial outlet port to provide communication from the gap to thehousing heavier material outlet port, the rotor including acommunication path for lighter material that extends from the gap andradially inwardly from the shell heavier material outlet port to theshell lighter material output port.
 9. The centrifugal separatoraccording to claim 8wherein said housing axis is a central axis, andwherein said rotor is rotatable concentrically about said central axis.10. A centrifugal separator according to claim 9, wherein the housinglighter material outlet port is concentric with the central axis.
 11. Acentrifugal separator according to claim 8, wherein the housing providesa biologically closed container.
 12. A centrifugal separator accordingto claim 8, wherein a gap is defined between the rotor and the housingand at least a portion of the gap between the rotor and housing is nogreater than the centrifugation gap.
 13. A centrifugal separatoraccording to claim 8, wherein at least a portion of the gap between therotor and the housing is smaller than the centrifugation gap.
 14. Acentrifugal separator according to claim 8, wherein the centrifugationgap provides a flow path between the at least one shell inlet port andthe at least one shell outlet port which is preferential to flowtherebetween through a gap defined between the housing and the rotor.